1. Field of Invention:
This invention relates generally to stereoscopic or three-dimensional displays, and more particularly to a system in which a three-dimensional image stored in a memory in terms of digital data is transformed into a three-dimensional spatial image.
2. State of Prior Art:
The operation of a two-dimensional electronic display for converting signals into visual imagery in real time depends on its ability to turn individual picture elements "ON" and "OFF" at a rapid rate. In an electronic display, the smallest controllable element is the pixel. Typically a high resolution, two-dimensional electronic display will have a quarter million pixels in an X-Y array, each being individually controllable to create a two-dimensional image whose pattern is defined by the activated pixels.
The concept of pixels operating in a flat panel display constituted by a matrix of LED's or other light-emitting elements has been extended to analog-raster-scan cathode ray tube (CRT) displays in which an electron beam is deflected to sweep across the phosphor face of the tube and thereby produce a luminous line. By digitally modulating the beam, one can then produce a linear string of illuminated dots, each corresponding to a pixel. Such pixels are created in all of the rows of the CRT raster. By varying the beam intensity, one can turn each pixel on and off or change its intensity.
There are various computer-aided systems which electronically store image data. Thus in computer-aided design (CAD), the computer functions to perform design calculations for determining optimum shape and size for a variety of applications ranging from three-dimensional mechanical structures to maps of huge areas.
By way of example, we shall consider computerized tomography or the CAT, which is an imaging technique in which the X-ray scanning beam of a computer-controlled X-ray scanner passes through the body of a patient and is collected by an array of detectors. The beam is rotated to produce a cross-sectional tomogram or slice through the body region of interest. By incrementally advancing the body relative to the X-ray scanner, a series of slices can be obtained.
The X-ray information collected through this rotary X-ray action is then used by the computer to reconstruct the internal structure. The resultant digital image is displayed on a CRT screen or recorded on film. In practice, the series of tomograms or slices may be sequentially displayed or recorded.
As pointed out in the 1984 Iwasaki U.S. Pat. No. 4,472,737, a diagnosis may be carried out by a doctor by observing the individual tomographs as they are sequentially displayed. But the doctor cannot actually see the internal structure in three dimensions. Thus, when tomographing a tumor in the head of a patient at a series of slice positions, the state of the tumor at each slice can be observed. However, the tumor as a whole cannot be viewed stereographically.
In this situation, the doctor, by exercising his imagination, and by observing several individual tomograms in sequence, can effectively combine these tomograms into a single stereographic image. Or the doctor, by observing tomograms taken at different angles spaced at proper angular intervals, can mentally synthesize the resultant slices to construct a single stereo image of the tumor. Thus the CAT provides individual two-dimensional tomograms which a skilled doctor can intellectually construct into a stereo image.
As Iwasaki recognizes, it is advantageous to present the doctor with an actual three-dimensional image in a computer-aided tomographic system. To this end, Iwasaki makes use of a digital memory to store tomographic picture data of several slices of the region of interest. This picture data is read out in sequence and at given time intervals on a cathode ray tube terminal. Interposed between the eye of the observer and the CRT screen are parallel liquid-crystal reproducer units. The reproducer units are sequentially actuated in synchronism with the CRT display so that each unit exhibits a respective slice. These reproduced slices are viewed in superposed relation to provide a stereo image of the region of interest.
The three-dimensional display disclosed in the 1977 Berlin U.S. Pat. No. 4,160,973 assigned to M.I.T. is interfaced with a computer to provide three-dimensional X-ray information in the medical field. The 3-D arrangement is also useful for nondestructive testing and in the field of computer-aided design. In the Berlin patent, an electronic two-dimensional display is provided, the display being constituted by a planar matrix of LEDs which are selectively activated by digital data derived from a computer to produce a two-dimensional image. The two-dimensional display is rotated while the LEDs are modulated to produce a three-dimensional image.
In the three-dimensional display disclosed in the 1984 Thomason et al. U.S. Pat. No. 4,462,044, a two-dimensional image is produced on the face of a cathode ray tube. An observer sees a reflection of this CRT image on the face of a vibrating mirror which is maintained in sinusoidal vibration. As the mirror vibrates through concave and convex positions, the image on the CRT screen appears closer and farther away from the observer with the apparent depth range being dependent on the amplitude of mirror vibrations.
Another 3-D approach to diagnostic imaging is that taken by Mezrich et al., U.S. Pat. No. 4,297,009, in which film transparencies of the cross-sectional slices of a given organ are mounted at sequential positions on a rotating disc, the images being intermittently illuminated to provide a 3-D display.
In the 3-D display disclosed in the Fajans U.S. Pat. No. 4,315,280, the information displayed is derived from a radar system which tracks an airplane and yields information which gives the plane location in space in x-y-z coordinates. Associated with the radar system is a cathode ray display terminal which produces a luminous spot at a position which is determined by the x-y coordinates of the airplane.
This luminous spot is projected into space by a rotating lens. The display is under computer control so as to render the spot luminous only when the lens is so oriented as to project the spot in space at a Z position corresponding to the instantaneous z position of the aircraft. The Fajans patent, therefore, does not provide three-dimensional images of the objects, but only a luminous spot in space whose x-y-z location is indicative of the instantaneous coordinates of the moving aircraft.
In the Fajans system, a potentiometer is operatively coupled to the rotating lens to provide an analog voltage indicative of th instantaneous angle of the lens. This mechanical arrangement has practical drawbacks, among which is the fact that the analog voltage must be converted into a digital value for processing in a computer.